1. Technical Field
The present invention relates to devices and methods for use in orthopedic spine surgery. In particular, the present invention relates to a device having at least two distinct articulating surfaces, the device being useful as an artificial disc replacement and a method of implanting that device using a posterior approach.
2. Background Art
The human spine is comprised of thirty-three vertebrae at birth and twenty-four as a mature adult. Between each pair of vertebrae is an intervertebral disc, which maintains the space between adjacent vertebrae and acts as a cushion under compressive, bending and rotational loads and motions. A healthy intervertebral disc has a great deal of water in the nucleus pulposus—the center portion of the disc. The water content gives the nucleus a spongy quality and allows it to absorb spinal stress. Excessive pressure or injuries to the disc can cause injury to the annulus—the outer ring that holds the disc together. Generally, the annulus is the first portion of the disc that seems to be injured. These injuries are typically in the form of small tears. These tears heal by scar tissue. The scar tissue is not as strong as normal annulus tissue. Over time, as more scar tissue forms, the annulus becomes weaker. Eventually this can lead to damage of the nucleus pulposus. The nucleus begins to lose its water content due to the damage—it begins to dry up. Because of water loss, the discs lose some of their ability to act as a cushion. This can lead to even more stress on the annulus and still more tears as the cycle repeats itself. As the nucleus loses its water content it collapses, allowing the two vertebrae above and below to move closer to one another. This results in a narrowing of the disc space between the two vertebrae. As this shift occurs, the facet joints located at the back of the spine are forced to shift. This shift changes the way the facet joints work together and can cause problems in the facet joints as well.
When a disc or vertebrae is damaged due to disease or injury standard practice is to remove part or all of the intervertebral disc, insert a natural or artificial disc spacer or interbody and construct an artificial structure to hold the effected vertebrae in place to achieve a spinal fusion.
A major challenge of spine surgery is in the development of surgical instruments for the surgeon to use during the implantation of the devices such as an artificial disc replacement or interbody. The instrumentation must be easy to use, effective, durable and most importantly, must not interfere with or cause further damage to the patient's anatomy.
There is a particular need to provide a specifically designed surgical instrument that can safely be used in the process of implanting a disc spacer or interbody between adjacent vertebrae and then easily disengage the instrument from the implanted interbody.